Using Radiogenic Noble Gas Isotopes to Characterize Subsurface Hydrocarbon Migration

Abstract

There is a complex and intimate association between the tectonics of fold-thrust belts, the deformation of foreland basins, and the generation and migration of hydrocarbons and other geologic fluids in the subsurface. Accurately characterizing the relationship between these factors, specifically understanding how deformation features will regulate hydrocarbon migration, is critical to predicting the economic success of conventional and unconventional energy plays. Noble gas geochemistry provides an underutilized geochemical technique to evaluate the fundamental properties of hydrocarbon gas migration. Because the initial ratios of radiogenic noble gases can be predicted by measuring the relative abundance of parent isotopes (U, Th, and K), the relative distribution of radiogenic isotopes in crustal minerals can provide important insight into the behavior of fluids in the crust. The 4He/21Ne* is particularly useful because the co-production of each isotope is fixed at 4He/21Ne*=22 × 106. Following radiogenic/nucleogenic production, the rate of diffusional release of each radiogenic isotope (i.e., 4He*, 21Ne*, and 40Ar*) from mineral grains in the rock matrix varies as a function of temperature. As a result, measuring the 4He/21Ne* or 4He/40Ar* in fluids or rocks provides information on effective rock porosity, temperature, and the rate and volume of fluid flow. Here, we examine the 4He, 21Ne*, 40Ar* concentrations and their isotopic ratios in crustal minerals from the Marcellus (Appalachian Basin), Eagle Ford (Western Gulf Basin), Barnett (Fort Worth Basin), and Bakken (Williston Basin) Formations. Samples include outcrop samples, subcrop samples collected at differing deformation regimes, and from core from the lateral legs of producing wells; each sample type experienced differing levels thermal maturity associated with their geological burial histories. Our results reflect fractionation of 4He and 21Ne* according to the thermal maturity of each sample set and proximity to deformational features.

AAPG Datapages/Search and Discovery Article #90259 ©2016 AAPG Annual Convention and Exhibition, Calgary, Alberta, Canada, June 19-22, 2016